The present invention relates to a projection display apparatus for enlarging a screen image, e.g., a television image, of an electro-optical display device.
U.S. Pat. Nos. 3,844,650 and 3,895,866 describe conventional apparatuses for enlarging and projecting images on the liquid crystal devices.
In these conventional apparatuses, a liquid crystal display device is irradiated with beams, and an image on the screen device is enlarged by a projection lens. The enlarged image is then projected on a screen.
However, a countermeasure against a temperature rise caused by high-intensity illumination light from a light source is not taken. When an image dynamically displayed on an electro-optical display device is enlarged and projected on a screen, the display device must be maintained within a predetermined temperature range, and short response time must be assured upon an application of electric energy.
In order to maintain the liquid crystal display device within the allowable operating temperature range, it is inconvenient to use a high-intensity beam. However, unless a high-voltage arc lamp such as a xenon lamp having a high intensity is used, good contrast of the display image to be projected on the screen cannot be obtained. This is apparent from the following considerations. A contrast ratio of the liquid crystal display device is very low as compared with an image printed on a film, and transmittance of the liquid crystal display device is a maximum of about 50%.
In a conventional projection display apparatus using an electro-optical display device, an indispensable technical issue for practical applications is the maintenance of the display device within the predetermined temperature range.
In order to enlarge and project a display image at a proper magnification (e.g., 20 to 30 times), image formation beams projected on the display device must be collimated beams. At the same time, it is also important not to display a shadow of a light-emitting portion of a lamp on the screen.
These problems are left unsolved in the conventional projection display apparatuses.